1. Field of the Invention
This invention relates to cationic surfactants which are useful for enhancing or potentiating the taste of sodium chloride and other salty tasting compounds by humans.
2. The Prior Art Environment
Sodium chloride, ordinary table salt, is an important component in many of the physiological processes of the human body. The chemical also imparts a more palatable taste to foods, and in fact, many foods are considered to be tasteless in the absence of salt. Unfortunately, it is also well known that there are diseases of the human body where the intake of salt in even ordinary amounts can adversely affect the control of the disease. In such instances, the intake of sodium chloride must be regulated. Hypertension and diabetes are examples of diseases where the regulation of sodium chloride intake is essential. Individuals who must regulate their salt intake are presented with the difficult problem of flavoring their foods so as to make the same palatable at low salt levels.
One of the methods available for regulating the intake of sodium chloride, is to substitute potassium chloride for ordinary table salt. But potassium chloride and most other substitutes for sodium chloride are inadequate in that the taste of the substitute is generally perceived as being different from table salt. And frequently bitter aftertastes are experienced. Accordingly, a satisfactory substitute for sodium chloride is highly desirable.
Another approach to the regulation of sodium chloride intake is to consume amounts that can be tolerated without injury to an individual's health. Investigators have been well aware that if the taste of low sodium chloride levels could somehow be enhanced or potentiated, the related problems of regulation of sodium chloride intake and maintenance of food palatability would be solved or at least minimized. However, only recently have significant advances been made in understanding the physiology of salt taste perception, an area that is vital to the investigation of salt taste enhancement. Research conducted by the present inventors, in cooperation with others, in an effort to elucidate the physiology of taste perception, has resulted in a breakthrough by establishing (1) the existence of lingual sodium channels across the lingual tissue and (2) the movement of sodium ions through such channels and across the lingual tissue as an electrical current, a discovery that was contra-indicated by previously prevailing theory. This discovery was reported in Science, Vol. 214, pp. 1039-41, Nov. 27, 1981, which reference is incorporated herein in its entirety. Subsequently, investigations by the inventors has correlated their breakthrough discovery with taste nerve response, and such correlation has been independently verified by other investigators in the field. See Soeda et al., Japanese Journal of Physiology, 35, 1101-1105, 1981; S. A. Simon & J. L. Gavin, "Salt & Acid Studies on Canine Lingual Epithelium", 398-408, American, Physiological Society, 1985.
In applying these discoveries to salt taste enhancement and/or potentiation, workers in the field have been searching for satisfactory compounds to increase sodium transport across lingual epithelium as a mechanism for potentiating the taste of sodium chloride. Schiffman et al. reported in their article, "Bretylium Tosylate Enhances Salt Taste", Physiology & Behavior, Vol. 36, 1129-1137 (1986) that bretylium tosylate enhances salt taste in humans and rats as statistically determined in human taste tests and as measured from electrophysiological taste responses in rats. However, bretylium tosylate has no effect on the short circuit current in isolated dog lingual epithelium, apparently acting through other physiological pathways. Bretylium tosylate is (obromobenzyl) ethyldimethylammonium p-toluenesulfonate, an ethical drug dispensed for the treatment of serious coronary heart disease. It is an adrenergic blocking agent which exhibits toxic side effects. As a result, the drug is of doubtful use as a salt taste enhancer.
Tada et al., J. Agric Food Chem., 32, 992-996 (1984) have reported on a group of polypeptides that exhibit a salty taste. It has been found that these compounds also exhibit a bitter taste component, and while they may possibly be used alone as salt substitutes, they have not been shown to potentiate or enhance salt taste.
Other problems faced by investigators in the development of salt taste potentiators include the requirement that the compound must be essentially non-reactive on the tongue except for the activity shown in taste enhancement; the compound must be chemically stable; it must be relatively non-toxic; it must be physically and chemically compatible with foods and beverages; and it must be economical.